Exhaust gas cleaning system for multi-cylinder internal combustion engine

Abstract

A motorcycle comprising a frame on which are mounted a fuel tank, a seat, front and rear wheels, and a multi-cylinder internal combustion engine disposed in a space defined by the fuel tank, seat and wheels. The engine has a plurality of exhaust ports open at the front of the engine connected to an exhaust system. An exhaust gas cleaning system is provided for the multi-cylinder internal combustion engine and comprises a reed valve assembly on the engine operating in response to pulsating exhaust pressure in the engine for selectively connecting an upstream secondary air passage connected to an inlet port of the reed valve assembly and a plurality of downstream secondary air passages of substantially equal length connected between outlet ports of the reed valve assembly and corresponding exhaust ports of the engine.

What is claimed is: 
     
       1. In a motorcycle having a frame with a longitudinal axis and on which are mounted a fuel tank and a seat; front and rear wheels suspended from said frame and a multi-cylinder internal combustion engine disposed in a space defined by said fuel tank, said seat and said wheels such that a crank shaft of said engine extends at right angles to the longitudinal axis of said frame, said engine including combustion chambers defined in respective cylinders, a plurality of exhaust ports open in the front of said engine and communicating with respective combustion chambers and exhaust means connected to respective exhaust ports; an improvement comprising an exhaust gas cleaning system for said multi-cylinder internal combustion engine including:   reed valve means on said engine having inlet and outlet ports and operating in response to pulsating exhaust pressure in said engine;   an upstream secondary air passage connected to said inlet port of said reed valve means and adapted to communicate with the atmosphere to supply secondary air to said reed valve means;   and a plurality of downstream secondary air passages of substantially equal length connected between said outlet ports of said reed valve means and corresponding exhaust ports of said engine to supply secondary air to said exhaust ports, said engine further including a cylinder head and a head cover, said reed valve means including a valve housing mounted on said head cover and defining a valve chamber therewith, and a reed valve in said valve housing dividing said valve chamber into an upstream and a downstream chamber which are connected respectively, to said upstream secondary air passage and said downstream secondary air passages.   
     
     
       2. An exhaust gas cleaning system as claimed in claim 1, wherein said reed valve means is disposed centrally, widthwise, on said head cover. 
     
     
       3. An exhaust gas cleaning system as claimed in claim 2 wherein said head cover has front and rear surfaces, said downstream secondary air passages extending along the front surface of said head cover to be cooled during forward travel of the motorcycle. 
     
     
       4. An exhaust gas cleaning system as claimed in claim 1 wherein said downstream secondary air passages are integral with said head cover. 
     
     
       5. An exhaust gas cleaning system as claimed in claim 4 wherein said head cover includes a space surrounding at least a part of said downstream secondary air passages and communicating with ambient air. 
     
     
       6. An exhaust gas cleaning system as claimed in claim 3,4 or 5 comprising cooling fins on said cover around said downstream secondary air passages. 
     
     
       7. An exhaust gas cleaning system as claimed in claim 1 comprising heat-resisting elastic packing means mounting said reed valve in said valve housing. 
     
     
       8. An exhaust gas cleaning system as claimed in claim 7 wherein said reed valve includes a plurality of reeds, one for each downstream secondary air passage. 
     
     
       9. An exhaust gas cleaning system as claimed in claim 8 comprising a partition dividing said space so that each reed controls flow of secondary air to its respective downstream secondary air passage, said partition extending towards said inlet port and tapering in thickness theretowards to divide the flow of incoming secondary air to the upstream chambers of the reeds. 
     
     
       10. An exhaust gas cleaning system as claimed in claim 1 wherein said valve chamber has an inlet port and a plurality of outlet ports corresponding to the downstream secondary air passages, each of said downstream secondary air passages including a first passage disposed in said head cover communicating with a respective outlet port of said valve chamber and a second passage disposed in said cylinder head and communicating with the associated exhaust port, and connecting means connecting said first and second passages in series in airtight manner. 
     
     
       11. An exhaust gas cleaning system as claimed in claim 10 wherein said connecting means includes a connecting member comprising a first end portion fitted into said downstream secondary air passage in said cylinder head in airtight manner and a second end portion fitted in airtight manner in said downstream secondary air passage in said head cover, one of said end portions being of larger diameter than the other. 
     
     
       12. An exhaust gas cleaning system as claimed in claim 11 wherein said connecting member includes a cylindrical body made of a material having relatively low heat conductivity, said cylindrical body having an inner peripheral surface and a heat-resistant metallic material on said inner peripheral surface. 
     
     
       13. An exhaust gas cleaning system as claimed in claim 11 wherein said one end portion of larger diameter of said connecting member is secured in its respective member and the other end of smaller diameter is sealably and slidably inserted into its respective member. 
     
     
       14. An exhaust gas cleaning system as claimed in claim 13 wherein each connecting member interconnects said first and second passages of the respective downstream secondary air passage, the connecting members of the plurality of downstream secondary air passages constituting a guide means for assembly of said head cover and cylinder head. 
     
     
       15. An exhaust gas cleaning system as claimed in claim 1 wherein each said downstream secondary air passage has a substantially constant cross-sectional area over the entire length thereof, said system further comprising a connecting pipe having an orifice connecting said inlet port of said reed valve means to said upstream secondary air passage. 
     
     
       16. A secondary air supply system of an exhaust gas cleaning system for an engine including a body having a plurality of cylinders and exhaust pipes connected to said cylinders, said secondary air supply system comprising secondary air supply passage means for supplying said exhaust pipes with secondary air and valve means disposed in an intermediate portion of said secondary air supply passage means for being opened and closed in response to pulsating exhaust pressure generated in said exhaust pipes, said secondary air supply passage means having an inlet end adapted for communication with the ambient atmosphere and an outlet end connected to said exhaust pipes, said valve means including a plurality of independent valve chambers corresponding to respective cylinders, a single valve housing having a secondary air inlet port through which secondary air is distributed to said valve chambers, said valve housing having an open lower face which is attached to said engine body, an insulator interposed between said lower face of said valve housing and said engine body, said valve housing and engine body cooperating to form said valve chamber, and a plurality of reed valves dividing each valve chamber into a upstream chamber and a downstream chamber, said upstream chambers being connected by said secondary air inlet port with the inlet end of said secondary air passage means, each of said downstream chambers being in communication with the outlet end of said secondary air passage means. 
     
     
       17. A secondary air supplying system as claimed in claim 16 wherein said insulator is a heat-resistant shock-absorbing material. 
     
     
       18. In a motorcycle having a frame suspending an internal combustion engine as a driving power source, said engine including a cylinder and cylinder head cover, said engine having an exhaust system, said frame having a head pipe and a main frame extending rearwardly from the head pipe immediately above said engine, and an exhaust gas cleaning system including a secondary air supply system connected to said exhaust system, and reed valve means interposed at an intermediate portion of said secondary air supply system for being opened and closed during engine operation to supply said exhaust system with secondary air to oxidize and remove unburnt components in said exhaust system, the improvement wherein said reed valve means is mounted on the head cover of said engine to constitute the upper profile of the engine, said main frame being shaped in correspondence with said upper profile to form a gap therewith of substantially uniform height. 
     
     
       19. A motorcycle as claimed in claim 18 wherein said head cover is removably attached to said cylinder, said gap being of a height to enable removal of said head cover and the reed valve means thereon as a unit from said cylinder.